From 144670893eccd84d638951f6c5bae43fc97e3c7b Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter@wuille.net>
Date: Fri, 28 Jan 2022 18:23:54 -0500
Subject: [PATCH] Abstract out verify logic for fe_get_b32

---
 src/field.h            | 6 +++++-
 src/field_10x26_impl.h | 6 +-----
 src/field_5x52_impl.h  | 6 +-----
 src/field_impl.h       | 7 +++++++
 4 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/src/field.h b/src/field.h
index b1c434eaf6b7f..327e63fc96fd8 100644
--- a/src/field.h
+++ b/src/field.h
@@ -86,6 +86,7 @@ static const secp256k1_fe secp256k1_const_beta = SECP256K1_FE_CONST(
 #  define secp256k1_fe_is_odd secp256k1_fe_impl_is_odd
 #  define secp256k1_fe_cmp_var secp256k1_fe_impl_cmp_var
 #  define secp256k1_fe_set_b32 secp256k1_fe_impl_set_b32
+#  define secp256k1_fe_get_b32 secp256k1_fe_impl_get_b32
 #endif /* !defined(VERIFY) */
 
 /** Normalize a field element.
@@ -185,7 +186,10 @@ static int secp256k1_fe_cmp_var(const secp256k1_fe *a, const secp256k1_fe *b);
  */
 static int secp256k1_fe_set_b32(secp256k1_fe *r, const unsigned char *a);
 
-/** Convert a field element to a 32-byte big endian value. Requires the input to be normalized */
+/** Convert a field element to 32-byte big endian byte array.
+ * On input, a must be a valid normalized field element, and r a pointer to a 32-byte array.
+ * On output, r = a (mod p).
+ */
 static void secp256k1_fe_get_b32(unsigned char *r, const secp256k1_fe *a);
 
 /** Set a field element equal to the additive inverse of another. Takes a maximum magnitude of the input
diff --git a/src/field_10x26_impl.h b/src/field_10x26_impl.h
index 5e0b65d652278..c3f49c86eb0dc 100644
--- a/src/field_10x26_impl.h
+++ b/src/field_10x26_impl.h
@@ -314,11 +314,7 @@ static int secp256k1_fe_impl_set_b32(secp256k1_fe *r, const unsigned char *a) {
 }
 
 /** Convert a field element to a 32-byte big endian value. Requires the input to be normalized */
-static void secp256k1_fe_get_b32(unsigned char *r, const secp256k1_fe *a) {
-#ifdef VERIFY
-    VERIFY_CHECK(a->normalized);
-    secp256k1_fe_verify(a);
-#endif
+static void secp256k1_fe_impl_get_b32(unsigned char *r, const secp256k1_fe *a) {
     r[0] = (a->n[9] >> 14) & 0xff;
     r[1] = (a->n[9] >> 6) & 0xff;
     r[2] = ((a->n[9] & 0x3F) << 2) | ((a->n[8] >> 24) & 0x3);
diff --git a/src/field_5x52_impl.h b/src/field_5x52_impl.h
index b06b485b7fc86..0994087c56af6 100644
--- a/src/field_5x52_impl.h
+++ b/src/field_5x52_impl.h
@@ -283,11 +283,7 @@ static int secp256k1_fe_impl_set_b32(secp256k1_fe *r, const unsigned char *a) {
 }
 
 /** Convert a field element to a 32-byte big endian value. Requires the input to be normalized */
-static void secp256k1_fe_get_b32(unsigned char *r, const secp256k1_fe *a) {
-#ifdef VERIFY
-    VERIFY_CHECK(a->normalized);
-    secp256k1_fe_verify(a);
-#endif
+static void secp256k1_fe_impl_get_b32(unsigned char *r, const secp256k1_fe *a) {
     r[0] = (a->n[4] >> 40) & 0xFF;
     r[1] = (a->n[4] >> 32) & 0xFF;
     r[2] = (a->n[4] >> 24) & 0xFF;
diff --git a/src/field_impl.h b/src/field_impl.h
index 304c428cb7490..a09c7a6be15fc 100644
--- a/src/field_impl.h
+++ b/src/field_impl.h
@@ -246,6 +246,13 @@ SECP256K1_INLINE static int secp256k1_fe_set_b32(secp256k1_fe *r, const unsigned
     secp256k1_fe_verify(r);
     return ret;
 }
+
+static void secp256k1_fe_impl_get_b32(unsigned char *r, const secp256k1_fe *a);
+SECP256K1_INLINE static void secp256k1_fe_get_b32(unsigned char *r, const secp256k1_fe *a) {
+    secp256k1_fe_verify(a);
+    VERIFY_CHECK(a->normalized);
+    secp256k1_fe_impl_get_b32(r, a);
+}
 #endif /* defined(VERIFY) */
 
 #endif /* SECP256K1_FIELD_IMPL_H */